This work is aimed at developing and establishing modern techniques of electron spin resonance (ESR) as general analytical tools for a wide range of biomedical studies. Recent years have witnessed an explosive growth in new ESR techniques, which have considerable potential for biomedical research but require further development. This work will build upon the pioneering efforts in the laboratory of Freed in four specific areas: (1) The new technique of two-dimensional Fouriertransform ESR (2D-FT-ESR) will be improved in sensitivity and resolution as required for biological systems. It will be developed for structural studies in biological materials based upon the nuclear modulation patterns arising from electron-nuclear hyperfine interactions, with sharply increased resolution over conventional 1D methods. The method will be extended to the study of spin-spin distances in multiply labeled biopolymers. 2D-FT-ESR will be developed to enhance the sensitivity of ESR to the motions of biomolecules. This will also provide a new means of separating out overlapping spectral components using their different rates of motion and will enable measurement of rates of exchange between different chemical environments in biological materials. (2) Fouriertransform (FT)-ESR Imaging techniques will be developed for the measurement of macroscopic lateral diffusion in biological systems. FT-ESR methods for spectral-spatial imaging kill also be developed for investigating microscopic dynamics in a variety of biological transport phenomena. These efforts will be directed to significantly improve upon previous cw-ESR imaging methods, and will include the extension to 2D-FT-ESR imaging. (3) High frequency (far-infrared) ESR will be developed for application to a variety of biological materials including spin-labelled proteins, lipids, and metalloproteins. This effort will be directed to improve the sensitivity of ESR to magnetic parameters, molecular ordering, and molecular motion. (4) Advanced algorithms for ESR spectral calculation will be developed for application to the new 2D-FT-ESR methods to enhance the effectiveness of motional and structural studies. New, more detailed models of molecular dynamics will be incorporated into the analysis of the ESR experiments on biological samples as required to enhance their interpretation.